The invention relates to pressure sensitive adhesive formulations. In particular, the invention relates to a pressure sensitive adhesive formulation comprising an acrylic polymer and a mixture of at least two substantially different tackifiers.
Typical acrylic pressure sensitive adhesive formulations are copolymers of alkyl ester monomers, a functional monomer such as acrylic acid, and may be crosslinked using, for example, aluminum chelates. While these adhesives are inherently tacky, they are generally deficient in adhesion to low energy surfaces. It is known in the art that adhesives may be tackified with e.g., rosin esters to improve low surface energy adhesion. Such tackification, however, typically results in loss of heat resistance. Furthermore, prior art tackified adhesives are deficient in anchorage to many tape backings.
There remains a need for improved polymer compositions which can be used to prepare pressure sensitive adhesives having sufficient adhesion to a variety of backing materials, particularly foam, and adhere to a wide variety of substrates, including low energy surfaces, while maintaining performance properties. The present invention addresses this need.
The invention provides adhesive formulations that exhibit very good adhesion to foam facestocks that are traditionally hard to bond and adhere to a wide variety of substrates, including low energy surfaces, while maintaining performance properties. The adhesives give unexpectedly high peel and tack at room and elevated temperatures.
One aspect of the invention is directed to a pressure-sensitive adhesive comprising an acrylic polymer and a mixture of at least two substantially different tackifiers. The tackifiers useful in the practice of the invention include at least one tackifier having a softening point of greater than about 60xc2x0 C. and at least another tackifier having a softening point of less than about 40xc2x0 C. In a preferred embodiment of the invention the adhesive comprises at least one rosin ester and at least one phenolic modified terpene.
In one embodiment, the adhesive comprises an acrylic polymer comprising at least one low glass transition temperature (Tg) alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group. The acrylic polymer may optionally comprise other monomers, including monomers having a high glass transition temperature and/or functional monomers. The acrylic polymer may, preferably, also comprise a crosslinking agent.
In a particularly preferred embodiment, the adhesive comprises an acrylic polymer comprising 2-ethylhexyl acrylate, methyl acrylate, acrylic acid, and a crosslinking agent tackified with a mixture of a rosin ester and phenolic modified terpene.
Yet another aspect of the invention is directed to adhesive articles, e.g., industrial tapes, transfer films, and the like, comprising a pressure sensitive adhesive comprising a mixture of at least two substantially different tackifiers.